This invention relates to shaft mounting devices and in particular to devices for inhibiting resonant oscillations of a shaft.
A shaft which extends or projects outward from its mounting bearing, or extends over a considerable distance between bearings has a natural resonant vibrational frequency which depends primarily on the length, mass and stiffness of the shaft in addition to the flexibility of the bearings in which the shaft is mounted. The tendency of a shaft to enter into resonant vibrations is enhanced when the shaft bearings have bearing play, that is the shaft may be radially vibrated with respect to the structure to which it is mounted by the bearing. When a shaft is excited to vibrate at a frequency which is at or near its natural vibrational frequency, or harmonics of its natural vibrational frequency, the amplitude of shaft vibration will be significantly increased causing unwanted operational noise and in severe cases damage to the bearings.
One prior art technique for suppressing vibrations in a shaft is disclosed in published German patent application 1,187,500. That application discloses vibration suppressing intermediate bearings in a curved drive shaft. The curvature of the drive shaft causes a shifting in the first mode resonant frequency of the drive shaft to a range higher than the anticipated revolution frequency of the shaft. Intermediate bearings are provided in the drive shaft at the point of maximum amplitude of vibration, to suppress vibrations of the second resonant mode. The intermediate bearings are supported within a tube containing the drive shaft by diametrically opposed rubber plugs. The operation of the rubber mounted intermediate support bearings is to directly suppress vibrations and not to affect the actual resonant frequency of the shaft in the second mode. The arrangement illustrated in the published application, while effective for the purpose disclosed, is not suitable for suppressing vibrations in an extended shaft, since the diametrically opposed rubber plugs suppress vibrations in only two radial directions.
A similar arrangement, wherein a bearing is mounted by resilient means is disclosed in German patent 1,160,310. The patent shows a bearing which is completely supported by resilient elements. Such a mounting while reducing the transmission of shaft vibrations to the structure on which the shaft is mounted does not alter the natural frequency of resonance of the shaft to reduce the amplitude of vibrations and consequently eliminate the source of vibrational noise and the possibility of excess bearing wear on account of shaft vibration. Also the structure disclosed does not effect the vibrational freedom resulting from bearing play.
It is therefore an object of the present invention to provide a shaft mounting which suppresses shaft vibrations.
It is a further object of the present invention to provide such a mounting which is economically constructed and easily assembled.